var fs = require('fs');
fs.readFile('D:\\test\\A.txt', function (err, data1) {
    fs.readFile('D:\\test\\B.txt', function (err, data2) {
        fs.readFile('D:\\test\\C.txt', function (err, data3) {
            console.log(data1 + '>>>' + data2 + '>>>' + data3);
            fs.writeFile('D:\\test\\D.txt', data1 + '>>>' + data2 + '>>>' + data3, function (err) {
                console.log(err);
            });
        });
    });
});
